1. Field of the Invention
The present invention relates to a device and a method for power supply switching, more particularly, to a device and method of switching voltages applied to security devices.
2. Discussion of Related Art
Viewers of cable television systems typically access cable content via a set-top box. The set-top boxes are usually equipped with conditional access and security circuitry for selective access to premium services such as pay-per-view.
The conditional access and security circuitry may be encapsulated in a replaceable security device such as a point of deployment (POD) module, smart card, etc. In this way, the security system can be upgraded or replaced over time without impacting the set-top box of a cable system.
While the security device is replaceable and different conditional access cards can be plugged into each individual module, different modules and cards require different bias voltages.
Further, when certain security device and conditional access cards are selected, different modes of a module require different voltage supplies. For example, except in standby mode, the Vcc pins of the security device should be supplied with 3.3V, while different voltages are needed for other modes of operation.
A need therefore exists for a device which can supply different voltages to a security device. There is a further need for a switching power supply device capable of sensing the change of voltage requirement when a security device is replaced or a different conditional access card is used for operation in different modes.
A device is provided for varying bias voltages to a security device in a cable set-top box, comprising a receiving unit in the security device for receiving replaceable conditional access cards, a card interface for sensing the insertion of conditional access cards in the receiving unit and outputting an enable signal to a logic unit, and the card interface for identifying a bias voltage of the conditional access card and outputting a request of the bias voltage to a controller, a controller for receiving the request of bias voltage from the card interface and outputting a selection signal of the bias voltage to a logic unit, the logic unit for receiving the enable signal from the card interface and selection signal of the bias voltage from the controller to output a control signal to a switch, and a switch for receiving a control signal from the logic unit and providing a switched voltage to the security device based on the selection signal from the controller.
A method for providing Vcc voltages to a security device in a cable set-top box, comprising the steps of receiving a replaceable conditional access card in the security device, sensing a replacement of the conditional access card in the security device, identifying varying bias voltages of the conditional access card in the security device, providing an enable signal from a card interface, providing a selection signal of the bias voltage from a controller, combining the enable and selection signals in a logic unit, providing a control signal to a switch, and providing a switched voltage to a receiving unit in the security device based on the selection signal from the controller.